1. Field of the Invention
The present invention relates to methods and apparatus for introducing medical devices into a patient's venous system (i.e., veins, vascular system, vena cavae, etc.). More particularly, the present invention relates to a method and apparatus for introducing an extrapulmonary blood gas exchange device into a patient's venous system enabling blood to receive oxygen and release carbon dioxide.
2. The Prior Art
Thousands of patients in hospitals suffer from inadequate blood gas exchange, which includes both inadequate blood oxygenation and inadequate removal of carbon dioxide (CO.sub.2). These conditions are commonly caused by varying degrees of respiratory inadequacy usually associated with acute lung illnesses such as pneumonitis, atelectasis, fluid in the lung, or obstruction of pulmonary ventilation. Various heart and circulatory ailments such as heart disease and shock can adversely affect the flow of blood and thereby also reduce the rate of blood gas exchange.
Currently the most widely used methods of treating these types of blood gas exchange inadequacies involve increasing the flow of oxygen through the lungs by either increasing the oxygen concentration of the inspired gases or by mechanically ventilating the lungs. Both methods result in placing further strain on the lungs, which may be diseased and unable to function at full capacity. In order to allow diseased or injured organs to heal it is generally best to allow these organs a period of rest followed by a gradual increase in activity. The current methods for treating inadequate blood gas exchange, however, force the diseased or damaged lungs to work even harder rather than allowing them a period of rest and recovery.
Various devices have been developed which are capable, at least for a limited period of time, of taking over the gas exchange function of the lungs. Many extracorporeal blood oxygenators are in common use and are employed most frequently during heart surgery. These devices are capable of providing blood oxygenation sufficient to carry the patient through the surgical procedure. These oxygenators include devices which bubble oxygen into the blood as the blood flows through the device. This is usually followed by a section of the device which defoams the blood to make it acceptable for reinjection into the patient.
Another group of extracorporeal oxygenators employ gas permeable membranes. These devices take many different shapes and configurations; however, the basic concept of operation is the same in all of these devices. Blood flows on one side of the gas permeable membranes while an oxygen rich gas flows on the other side of the membrane. As the blood flows through the device, the oxygen travels across the gas permeable membrane and enters the blood. This allows oxygenation of the blood without actually introducing oxygen bubbles into the blood and without the corresponding need for an extensive defoaming apparatus.
Gas permeable membranes used in such extracorporeal oxygenators are of two types. One type uses a microporous membrane which allows blood gas interface through micropores in the membrane. The other type is a continuous membrane which does not have micropores but which allows blood gas exchange through the membrane without the blood gas interface.
The microporous and bubble oxygenators discussed above are not suited for use outside the setting of a cardiopulmonary bypass procedure, and are thus typically designed for short term extracorporeal use. As a result, these devices are of limited use in the long term intensive care of respiratory failure patients.
In vivo extrapulmonary blood gas exchange has been attempted in the art. One known device consists of a plurality of small diameter gas permeable tubes connected to headers at each end. The headers are connected on one end to a source of oxygen rich gas and on the other end to an exhaust means. The apparatus is positioned within the vena cavae by means of a two-step process. First, an incision is made in the patient's femoral or iliac vein or internal jugular vein and in the patient's jugular vein. A radiopaque guide catheter is inserted into the jugular vein and is guided through the superior and inferior vena cavae using a fluoroscope, so as to exit through the incision in the femoral or iliac vein or internal jugular vein. Second, the device is attached to the guide catheter and is pulled into the vena cavae by withdrawing the guide catheter from the jugular vein.
While the method of inserting this extrapulmonary blood gas exchange device within a patient's vena cavae has been successfully demonstrated, still there are some drawbacks. First, the need for two incisions in the patient's venous system not only increases the complexity of the procedure but also subjects the patient to significant trauma and safety risk. In addition, the need to insert a guide catheter from the patient's jugular vein to the femoral or iliac vein or internal jugular vein exposes the patient to a serious risk of damaging the sensitive intimal tissues of the patient's venous system. Furthermore, the blood gas exchange device itself must have a small overall diameter to be able to pass through relatively narrow veins such as the jugular vein. As a result, when the device is within the vena cavae, which have a much larger diameter than the jugular vein, the blood flow bypasses the gas permeable tubes. Thus, blood contact with the surface of the gas permeable tubes is reduced.
In an attempt to avoid this problem, a spiral or undulating arrangement of the gas permeable tubes has been used. This increases the blood contact with the gas permeable tube surfaces. Also, the undulating or spiral arrangement of the gas permeable tubes reduces laminar blood flow through the vena cavae. Laminar blood flow is undesirable because such flow produces a boundary layer between the bulk flow of the blood and the surface of the gas permeable tubes. This boundary layer of blood significantly reduces gas transfer. The undulating or spiral arrangement of the gas permeable tubes offers limited improvement in performance of the device.
Recently, an in vivo extrapulmonary blood exchange device has been developed which is described in U.S. Pat. No. 4,850,958, entitled "Apparatus and Method for Extrapulmonary Blood Gas Exchange," issued Jul. 25, 1989. That device has a bundle comprising a plurality of gas permeable tubes bound at each end and enclosed within air tight proximal and distal chambers. The device also has a dual lumen tube with an outer lumen and an inner lumen which is situated relative to the gas permeable tubes such that the outer lumen terminates within the proximal chamber and such that the inner lumen terminates within the distal chamber. The outside diameter of the bundle of gas permeable tubes may be selectively adjusted to provide either a furled, small insertion diameter when inserting the apparatus into the vena cavae of a patient or an unfurled, expanded oxygenation diameter after the apparatus is in place within the vena cavae and the bundle of gas permeable tubes is deployed therein. Because the device is typically inserted into the patient through a single incision at one of the right external iliac, common femoral or internal jugular veins, care must be taken not to damage the delicate gas permeable tubes or the sensitive intimal tissues of the patient's venous system.
Over the years, sheaths and obturators have been used to assist in introducing various types of medical devices into a patient's body. Always, a major concern is the damage caused to the tissue surrounding the invasive path of the sheath, obturator, or medical device. An additional concern is the delicate handling of the medical device to avoid damage to the device which may inhibit its effectiveness. In inserting the particularly delicate in vivo blood gas exchange device referenced above, care must be taken not to snag, pinch, crush, or kink the gas permeable tubes. Sheaths and obturators which are known in the art are not suited to solve or minimize these concerns.